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Abstract:

Apparatus for laying conduit from a vessel comprises reel carrier
arranged to receive a reel (202) wound with conduit (204) and capable of
being reciprocated along the direction of the axis (214) of the reel as
the conduit is unwound. The apparatus further comprises a straightener
(208), and a control unit arranged to control the reel carrier such that
the fleet angle created between the conduit and the straightener is
reduced. Such an arrangement ensures that the conduit is not bent past
its limit of elastic deformability while allowing the straightener to be
situated relatively close to the reel.

Claims:

1. Apparatus for laying conduit from a vessel comprising a reel carrier
arranged to receive a reel wound with conduit and capable of being
reciprocated along the direction of the axis of the reel, a straightener,
and a control unit arranged to control the reel carrier during the laying
process such that the fleet angle created between the conduit and the
straightener is reduced.

2. Apparatus as claimed in claim 1, wherein the reel carrier is mounted
on rails.

3. Apparatus as claimed in claim 1, further comprising a hydraulic drive
unit arranged to reciprocate the reel carrier under the control of the
control unit.

4. Apparatus as claimed in claim 1, further comprising an electrical
drive unit arranged to reciprocate the reel carrier under the control of
the control unit.

5. Apparatus as claimed in claim 1, wherein the control unit is arranged
to control the reel carrier automatically in accordance with a
pre-programmed algorithm.

6. Apparatus as claimed in claim 1, further comprising a fleet angle
monitor arranged to measure the fleet angle between the pipe or cable and
the straightener, wherein the fleet angle monitor is associated with the
control unit, and the control unit is arranged to control the reel
carrier in accordance with the measured fleet angle.

7. Apparatus as claimed in claim 6, wherein the fleet angle monitor
includes a proximity switch.

8. Apparatus as claimed in claim 6, wherein the fleet angle monitor
includes a laser guide.

9. Apparatus as claimed in claim 1, wherein the straightener is movable
in the vertical plane.

10. Apparatus as claimed in claim 1, wherein the straightener is
pivotable about a horizontal axis.

11. Apparatus as claimed in claim 1, comprising a reel wound with conduit
mounted on the reel carrier.

13. A method of laying conduit from a reel on a vessel comprising the
steps of feeding the conduit from the reel through a straightener
reciprocating the reel along the axis of the reel such that as the
conduit is laid the fleet angle between the conduit and the straightener
is reduced.

14. A method as claimed in claim 13, wherein the fleet angle between the
conduit and the straightener is kept within the range from 0 to 5
degrees.

15. A method as claimed in claim 13, wherein the fleet angle between the
conduit and the straightener is kept within the range from 0 to 3
degrees.

16. A method as claimed in claim 13, wherein the reciprocation of the
reel is controlled by a control unit.

17. A method as claimed in claim 16, wherein the control unit
reciprocates the reel in accordance with a preprogrammed algorithm.

18. A method as claimed in claim 16, further including the steps of
measuring the fleet angle between the conduit and the straightener and
the control unit reciprocating the reel in accordance with the measured
fleet angle between the conduit and the straightener.

20. A method as claimed in claim 13, wherein the straightener is
vertically adjusted as the pipe or cable is unwound from the reel as the
pipe or cable is laid.

21. A vessel including the apparatus as claimed in claim 1.

22. A vessel for laying conduit according to the method as claimed in
claim 13.

23. A reel carrier for carrying a reel wound with conduit, wherein the
reel carrier may be reciprocated along direction of the axis of the reel.

Description:

TECHNICAL FIELD

[0001] The invention relates to, but not exclusively to, an apparatus and
method for laying pipe from a pipe laying vessel.

BACKGROUND OF THE INVENTION

[0002] Subsea pipes or cables are often laid from pipe or cable laying
vessels, where the pipes or cables are stored wound around a large reel
before they are laid. FIG. 1 shows an example of a prior art arrangement,
where a reel 100 of rigid pipe 102 is mounted on a reel carrier 104. In
an alternative prior art arrangement, the reel 100 may be a reel of
cable. The pipe 102 is unwound from the reel 100 and passed through a
straightener 106 and a tensioner 108 before it moves down a stinger 110
and is laid on the sea bed. The pipe 102 being laid, being a rigid pipe
stored on a reel, needs to be straightened and undergo plastic
deformation, by means of the straightener 106. Thus, as the pipe 102 is
unwound from the reel 100 the straightener 106 bends about a horizontal
axis the pipe 102 in order to straighten the pipe 102 from being curved
from being wound up around the reel 100. In order that the pipe 102 is
not bent about its vertical axis past its limit of elastic deformability,
the fleet angle between the pipe 102 and the straightener 106 must be
kept below a certain angle. FIG. 2 shows a plan view of the pipe laying
arrangement of FIG. 1, where the fleet angle is the angle θ created
between the pipe and the straightener due to the offset between the part
of the reel 100 from which the pipe 102 is being unwound and the position
of the straightener 106. As can be seen, the fleet angle will be greatest
when the pipe 102 is being unwound from the edges of the reel 100. When
the pipe 102 is directly in line with the straightener 106 the fleet
angle is 0 degrees. The fleet angle is always to be considered as a
positive angle, as a measure of the deviation away from the 0 degrees
when the pipe 102 is directly in line with the straightener 106,
regardless of which side of the straightener 106 the pipe 102 has been
deviated.

[0003]FIG. 2 shows a simplified version of how the pipe 102 travels from
the reel 100 to the straightener 106. In most cases, the pipe 102 will
actually be controlled so as to form an S-curve in the horizontal plane,
with the curvature being kept within the limits of the elastic bending
range. This adds further complexity to the pipe laying arrangement.
Despite the fact that the pipe 102 may not form a straight line between
where it leaves the reel 100 passes through the straightener 106, the
fleet angle can still be used as a measure of the offset between where
the pipe 102 leaves the reel 100 and meets the straightener 106.

[0004] A further disadvantage of having a large fleet angle is that when a
pipe or cable is being laid in an arrangement as described above, the
large fleet angle may lead to the pipe or cable wearing or becoming
damaged where it meets the straightener, leading to failure or reduced
working life of the pipe or cable.

[0005] In order to keep the fleet angle below a certain maximum angle the
reel 100 must be sited a relatively large distance from the straightener
106. In order to reduce this distance slightly, the straightener may be
in a "floating" type arrangement, where it is possible for it to move
from side to side as necessary and thereby help manage the fleet angle.
However, the distance between the straightener 106 and the reel 100 is
still large and the straightener arrangement may be complicated.

[0006] Also, the straightener must feed the pipe 102 to the tensioner 108
approximately straight on, with no significant fleet angle. Therefore, if
the straightener 106 is located closer to the reel 100 due to being in a
"floating" arrangement as described, the tensioner 108 must be located
further away from the straightener 106 to reduce the change in angle of
the pipe it receives due to the movement of the straightener.

[0007] The present invention seeks to at least partially mitigate or
overcome these disadvantages.

SUMMARY OF THE INVENTION

[0008] The present invention provides apparatus for laying conduit from a
vessel comprising a reel carrier arranged to receive a reel wound with
conduit and capable of being reciprocated along the direction of the axis
of the reel, a straightener, and a control unit arranged to control the
reel carrier during the laying process such that the fleet angle created
between the conduit and the straightener is reduced.

[0009] The axis of the reel is the axis around which the conduit is wound.
Advantageously, the reel carrier may be reciprocated as the conduit is
unwound such that the part of the reel from which the conduit is being
unwound is substantially in direct alignment with the straightener,
thereby reducing or eliminating any fleet angle between the conduit and
the straightener. Advantageously, the straightener can be located much
closer to the reel and reel carrier, thereby saving space on a pipe
laying vessel. The straightener may be located within 5 meters of the
reel and reel carrier. More preferably, the straightener may be located
within 3 meters of the reel and reel carrier. Advantageously, the closer
the straightener is located to the reel and reel carrier, the easier the
pipe is to control. Further advantageously, a reel of greater than
standard width may be used without the fleet angle becoming excessive.

[0010] The apparatus may be installed on a pipe laying vessel.
Alternatively, the apparatus may be installed on a multi-purpose support
vessel (MSV) in order to adapt the MSV into a pipe laying vessel.

[0011] The reel carrier may be mounted on rails. The rails may be mounted
traverse to the'direction of conduit lay. The reel carrier may include
wheels, rollers, low friction pads or air skates to enable the
reciprocating motion.

[0012] A hydraulic drive unit may be arranged to reciprocate the reel
carrier under the control of the control unit. Alternatively, the drive
unit may be pneumatic or electrically driven, or alternatively the reel
carrier may be driven by any other suitable means. The reel carrier and
the drive unit may be capable of handling large loads. The weight of the
reel including the weight of the pipe or cable may be 400 tonnes or more.
The weight of the reel excluding the weight of the pipe or cable may be
50 tonnes or more.

[0013] The control unit may control the reel carrier manually or
automatically. The control unit may include a central processing unit
(CPU) arranged to control the reel carrier in accordance with an
automatic pre-programmed algorithm. The pre-programmed algorithm may take
into account how the pipe is wound on the reel and how the circumference
of the reel reduces as the pipe is unwound. The control unit may be
adjustable to take into account different types of conduit and/or reels
being used. The control unit may be an entirely mechanical arrangement.
Alternatively, the control unit may comprise an input, the input may be
controlled by a person operating the apparatus or proximity switches.

[0014] The apparatus may further include a reel wound with conduit mounted
upon the reel carrier. The conduit may be a pipe for conveying fluids,
such as oil, or may be a tube or duct for enclosing electrical or fibre
optic wires or cables. The conduit may be an umbilical for controlling
subsea installations. The conduit wound around a reel may be a single
continuous length of pipe or may be a pipe created out of a plurality of
sections of pipe welded (or joined in any other suitable manner)
together. The pipe may be a rigid pipe. The pipe may be an insulated
pipe. The pipe may be suitable for carrying oil, gas, carbon hydrate or
water (fresh, seawater or produces water) in a subsea environment. A
typical pipe diameter may be from 3 inches (76 mm) to 8 inches (203 mm).
Alternatively, a pipe diameter may be from 2 inches (56 mm) to 18 inches
(457 mm) or more. The payout speed from the reel may be from 0 to 500
meters per hour. The payout speed may be greater than 500 meters per
hour.

[0015] A fleet angle monitor may be arranged to measure the fleet angle
between the conduit and the straightener. The fleet angle monitor may be
associated with the control unit. The control unit may be a CPU arranged
to control the reel carrier in accordance with the measured fleet angle.
The fleet angle monitor may be arranged such that when it detects that
the conduit is moving such that an undesirable fleet angle has been or
will be created between the conduit and the straightener the control unit
actuates the reel carrier in the appropriate direction in order to reduce
the fleet angle. The fleet angle monitor may include a proximity switch.
The fleet angle monitor may include a laser guide. Preferably, the reel
carrier is arranged to receive the reel with the reel axis in the
approximately horizontal plane.

[0016] The straightener may be movable in the vertical plane. The
straightener may be pivotable. The straightener may be pivotable in a
horizontal or vertical plane. The straightener may be restricted such
that it cannot move from side to side in a horizontal plane.
Advantageously, the straightener can compensate for the change of angle
caused as the conduit moves from being unwound from the outer part of the
reel to being unwound from the inner part of the reel. The straightener
may compensate for a change of angle by moving in a vertical plane and/or
pivoting in a horizontal plane. The straightener may be moved by a drive
unit or it may be in a floating arrangement and reactive to and driven by
the angle at which the conduit is presented to the straightener.

[0017] The invention further provides a method of laying conduit from a
reel on a vessel comprising the steps of feeding the conduit from the
reel through a straightener, and reciprocating the reel in a direction
along the axis of the reel such that as the conduit is laid the fleet
angle between the conduit and the straightener is reduced.

[0018] Advantageously, reciprocating the reel as the conduit is unwound
enables the fleet angle to be kept low or zero, so that the part of the
conduit being unwound from the reel is always approximately in line with
the straightener. Preferably, the fleet angle between the conduit and the
straightener is kept between the range from 0 to 5 degrees, more
preferably between 0 to 3 degrees and even more preferably between 0 and
1 degrees. Preferably, when viewed from above, the conduit appears to be
approximately straight as it passes through the straightener.

[0019] The reciprocation of the reel may be controlled by a control unit.
The control unit may reciprocate the reel manually or automatically. The
control unit may reciprocate the reel in accordance with an automatic
pre-programmed algorithm. The control unit may be a central processing
unit. The control unit may reciprocate the reel in accordance with the
measured fleet angle between the pipe or cable and the straightener. The
control unit may include proximity switches. The control unit may be an
entirely mechanical arrangement. Alternatively, the control unit may
comprise an input, the input may be controlled by a person operating the
apparatus.

[0020] The conduit being laid may be rigid pipe. A rigid pipe is typically
used when laying subsea pipes and the skilled man will appreciate that
such a rigid pipe is not entirely inflexible. The rigid pipe may be
plastically deformable to a limited extent. The rigid pipe may be
plastically deformable to the extent that it may be wound in a reel. The
rigid pipe may be elastically deformable to a limited extent.

[0021] The reel may be mounted on the vessel with its axis in a
substantially horizontal plane. The method may include the step of the
straightener being vertically adjusted as the pipe or cable is unwound
from the reel as the pipe or cable is laid. Advantageously, this
compensates for the change of angle of the pipe as it is unwound from the
outer part of the reel to the inner part of the reel. The pipe or cable
may be being laid in an S-lay or a J-lay configuration.

[0022] The apparatus may be capable of being installed on a vessel. The
vessel may be a multi-purpose support vessel. The invention also provides
a conduit laying vessel including the apparatus as described above. The
vessel may be a pipe or cable laying vessel. The invention also provides
a vessel suitable for performing a method of conduit laying as described
above.

[0023] The invention also provides a reel carrier for carrying a reel
wound with conduit, wherein the reel carrier may be reciprocated along
direction of the axis of the reel. The reel carrier may be installed on a
vessel, including a multi-purpose support vessel.

[0024] Where features of the invention have been described above in
relation to one aspect of the invention, they are equally applicable to
other aspects of the invention and vice versa.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Embodiments of the invention will now be described with reference
to the following figures, of which:

[0026]FIG. 1 shows a pipe-laying apparatus according to the prior art;

[0027]FIG. 2 shows a plan view of the pipe-laying apparatus of FIG. 1,
with particular reference to the fleet angle;

[0033]FIG. 8 shows a diagram of the control unit and measuring device in
relation to the reel carrier.

DETAILED DESCRIPTION

[0034]FIG. 3 shows a pipe laying vessel 200 including a reel 202 on which
a plastically deformable pipe 204 is wound. The reel 202 is mounted on a
reel carrier 206 with the axis of the reel in an approximately horizontal
plane and perpendicular to the direction of lay of the pipe. The pipe 204
is unwound and fed through a straightener 208, a tensioner 210 and then
down a stinger 212 as it is laid on the seabed. The straightener 208
bends the pipe 204 from the curved state which is caused by being wound
around the reel 202 into a state where it is approximately straight and
ready to be laid.

[0035]FIG. 4 shows a plan view of the apparatus shown in FIG. 3. The reel
carrier 206 is mounted on a set of rails 214, the rails 214 running
traverse to the deck of the vessel 200, such that the reel carrier 206
may be reciprocated between the port and starboard sides of the vessel
200. In this case, as shown in FIG. 7, the reel carrier 206 runs on a set
of wheels 216 mounted on the rails 214, though rollers or low friction
pads could be used.

[0036] The reciprocation of the reel carrier 206 between the port and
starboard sides of the vessel 200 is driven by a hydraulic drive unit
218. The hydraulic drive unit is controlled by a control unit 220, where
the control unit 220 is arranged to reciprocate the reel carrier 206 such
that the fleet angle created between the pipe 204 and the straightener
208 remains at approximately 0 degrees as the pipe 204 is laid. The
position of the reel carrier 206 on the rails 214 depends on the part of
the reel 202 that the pipe 204 is being unwound from at any particular
time.

[0037] As can be seen from FIG. 5, when the pipe 204 is being unwound from
the starboard side of the reel 202, the reel carrier is moved to the port
side of the rails 214. Similarly, it can be seen from FIG. 6 that when
the pipe is being unwound from the port side of the reel 202, the reel
carrier 206 is moved to the starboard side of the rails 214. It can be
seen from these figures that by reciprocating the reel carrier 206 in
this way, the fleet angle remains constantly approximately zero.

[0038]FIG. 8 shows the control unit 220 associated with a fleet angle
measuring unit 222. The fleet angle measuring unit 222 includes a pair of
proximity switches which monitor whether the fleet angle is deviating
from zero degrees as the reel 202 unwinds. If the fleet angle does
deviate from zero degrees then the control unit 220 activates the
hydraulic drive unit 218 to move the reel carrier 206 as appropriate.

[0039] It can also be seen that the distance between the straightener 208
and the reel 202 is considerably reduced in comparison to the distance in
the prior art arrangement. The distances in the prior art arrangement may
range between 15 m and 40 m. In the current embodiment, the distance
between the straightener may be 5 m or less. As a result of the
straightener 208 being close to the reel 204, it will be appreciated that
as the reel 202 unwinds, the vertical angle at which the pipe 204 is
presented to the straightener 208 varies. The pipe 204 shows the reel 202
towards the end of the laying process, when most of the pipe has been
unwound and the pipe is close to the centre of the reel 202. The pipe
204' shows the vertical angle of the pipe when the reel 202 is initially
unwound at the beginning of the laying process. The straightener can move
to adapt to the varying vertical angle, as can be seen, the straightener
initially being in the position indicated by 208'. In this case the
straightener 208 is in a floating arrangement, such that tension in the
pipe 204 moves the straightener 208 up or down as appropriate. The
straightener 208 is also pivotable about a horizontal axis to enable it
to adapt to the vertical angle of the pipe 204. In an alternative
arrangement to the straightener being in a floating arrangement, the
straightener may be driven by hydraulic or other means.

[0040] Whilst the present invention has been described and illustrated
with reference to particular embodiments, it will be appreciated by those
of ordinary skill in the art that the invention lends itself to many
different variations not specifically illustrated herein. By way of
example only, certain possible variations will now be described.

[0041] The invention may be used to lay cables rather than pipes,
particularly cables that require straightening before being laid once
they are unwound from a reel. The control unit may control the
reciprocation of the reel carrier automatically, with no input from a
measuring device. The control unit may control the reciprocation of the
reel carrier manually. For example, the control unit may be an entirely
mechanical unit, or include an input, such as a switch or lever which is
operable by an operator.

[0042] The invention has been described in relation to an S-lay
arrangement, with the pipe being unwound from the bottom of a reel.
Alternatively, the pipe may be unwound from the top of a reel. Further
alternatively, the invention may be applied to a J-lay arrangement. The
J-lay arrangement may include the pipe being routed through an
underbender and up into a J-lay tower. The J-lay arrangement may be a
conventional arrangement with the pipe being unwound from the top of a
reel.

[0043] It is to be understood that optional integers or features, whilst
of possible benefit in some embodiments of the invention, may not be
desirable, and may therefore be absent, in other embodiments. Any ranges
of parameters, variables, or other values quoted herein are intended to
cover the limits of the ranges inclusively.

Patent applications by SAIPEM UK LIMITED

Patent applications in class Facilitated by extension from line-laying vessel

Patent applications in all subclasses Facilitated by extension from line-laying vessel